Non-aqueous electrolyte solution for secondary batteries, and lithium ion secondary battery

Abstract

To provide a flame-retardant non-aqueous electrolyte solution for secondary batteries, with which a lithium ion secondary battery excellent in the rate properties can be obtained; and a safe lithium ion secondary battery excellent in the rate properties. A non-aqueous electrolyte solution for secondary batteries, comprising a lithium salt and a liquid composition, wherein the liquid composition comprises at least one fluorine-containing solvent (α) selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, and a cyclic carboxylic acid ester compound, the lithium salt contains LiPF 6 , and the lithium ion diffusion coefficient of the non-aqueous electrolyte solution at 25° C. is at least 1.1×10 −10 m 2 /s.

What is claimed is: 
     
         1 . A non-aqueous electrolyte solution for secondary batteries, comprising a lithium salt and a liquid composition, wherein
 the liquid composition comprises a fluorine-containing solvent (α) containing at least one member selected from the group consisting of a fluorine-containing ether compound, a fluorine-containing chain carboxylic acid ester compound and a fluorine-containing chain carbonate compound, and a cyclic carboxylic acid ester compound,   the lithium salt contains LiPF 6 , and   the lithium ion diffusion coefficient of the non-aqueous electrolyte solution at 25° C. is at least 1.1×10 −10  m 2 /s.   
     
     
         2 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the liquid composition has a viscosity of at most 1.7 mPa·s at 25° C. 
     
     
         3 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , which has a lithium salt content of from 0.7 to 1.5 mol/L. 
     
     
         4 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the cyclic carboxylic acid ester compound is at least one member selected from the group consisting of γ-butyrolactone, γ-valerolactone and ε-caprolactone. 
     
     
         5 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the ratio of the mass of the cyclic carboxylic acid ester compound to the total mass of the non-aqueous electrolyte solution is from 4 to 50 mass %. 
     
     
         6 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the ratio of the mass of the fluorine-containing solvent (α) to the total mass of the non-aqueous electrolyte solution is from 30 to 80 mass %. 
     
     
         7 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein N A /N Li , i.e. the ratio of the total number of moles N A  of the cyclic carboxylic acid ester compound to the total number of moles N Li  of lithium atoms derived from the lithium salt, is from 1.5 to 7.0. 
     
     
         8 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the liquid composition further contains at least one compound (β) selected from the group consisting of a saturated cyclic carbonate compound, a saturated chain carbonate compound having no fluorine atom, a saturated cyclic sulfone compound (excluding a lithium salt) and a phosphoric acid ester compound. 
     
     
         9 . The non-aqueous electrolyte solution for secondary batteries according to  claim 8 , wherein (N A +N B )/N Li , i.e. the ratio of the sum of the total number of moles N A  of the cyclic carboxylic acid ester compound and the total number of moles N B  of the compound (β) to the total number of moles N Li  of lithium atoms derived from the lithium salt, is from 3.0 to 7.0. 
     
     
         10 . The non-aqueous electrolyte solution for secondary batteries according to  claim 8 , wherein the ratio of the mass of the saturated chain carbonate compound having no fluorine atom to the total mass of the non-aqueous electrolyte solution is at most 30 mass %. 
     
     
         11 . The non-aqueous electrolyte solution for secondary batteries according to  claim 8 , wherein the ratio of the sum of the mass of the saturated cyclic carbonate compound and the mass of the saturated chain carbonate compound having no fluorine atom to the total mass of the non-aqueous electrolyte solution is at most 30 mass %. 
     
     
         12 . The non-aqueous electrolyte solution for secondary batteries according to  claim 1 , wherein the fluorine-containing solvent (α) contains the fluorine-containing ether compound. 
     
     
         13 . The non-aqueous electrolyte solution for secondary batteries according to  claim 12 , wherein the fluorine-containing ether compound is a compound represented by the following formula (1):
   R 1 —O—R 2   (1)
   
       wherein each of R 1  and R 2  which are independent of each other, is a C 1-10  alkyl group, a C 3-10  cycloalkyl group, a C 1-10  fluorinated alkyl group, a C 3-10  fluorinated cycloalkyl group, a C 2-10  alkyl group having at least one etheric oxygen atom, or a C 2-10  fluorinated alkyl group having at least one etheric oxygen atom, provided that one or each of R 1  and R 2  is a C 1-10  fluorinated alkyl group, a C 3-10  fluorinated cycloalkyl group or a C 2-10  fluorinated alkyl group having at least one etheric oxygen atom. 
     
     
         14 . The non-aqueous electrolyte solution for secondary batteries according to  claim 13 , wherein the compound represented by the formula (1) contains at least one member selected from the group consisting of CF 3 CH 2 OCF 2 CHF 2 , CF 3 CH 2 OCF 2 CHFCF 3 , CHF 2 CF 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 CH 2 OCF 2 CHF 2 , CH 3 CH 2 OCF 2 CHF 2  and CHF 2 CF 2 CH 2 OCF 2 CHFCF 3 . 
     
     
         15 . A lithium ion secondary battery comprising a positive electrode containing, as an active material, a material capable of absorbing and desorbing lithium ions, a negative electrode containing, as an active material, at least one member selected from the group consisting of metal lithium, a lithium alloy and a carbon material capable of absorbing and desorbing lithium ions, and the non-aqueous electrolyte solution for secondary batteries as defined in  claim 1 .